1. Field of the Invention
The present invention relates to a vehicle simulator.
Vehicle simulators are widely used in training or entertainment applications. One major area of use is in the training of aircraft pilots.
2. Related Art
In a typical aircraft flight simulator, a trainee pilot sits in a mock cockpit and views an image visible to him through the cockpit windows. Often the mock cockpit is supported on a motion platform so that the physical effects of vehicle motion can be simulated to supplement the simulation of aircraft motion represented by the visual image. Typically the mock cockpit is supported on a rigid platform that is itself supported on six hydraulic jacks. The hydraulic jacks are connected between three pivots on the underside of the platform and three pivots on a support base beneath the platform. Thus each platform pivot is connected to two jacks which are in turn connected to respective ones of a pair of the support base pivots. This conventional jack system provides six degrees of freedom and is the industry standard for motion platform support systems.
A variety of visual systems have been proposed for use in vehicle simulators. Generally such visual systems can be divided into two types, that is uncollimated and collimated.
In uncollimated systems, an image to be viewed by the simulator user is projected on to a screen or dome placed in front of the mock cockpit. The screen surface is typically between three and six meters from the simulator user's eyepoint and thus such systems are not ideally suited to portray images representing distant objects. Uncollimated systems are however often used where very wide fields of view are required as it is difficult to project images showing very wide fields of view using collimated systems. Uncollimated systems are also sometimes favoured for simulating vertical take off aircraft where it is necessary to train pilots in very low altitude manoeuvres. In such circumstances the short distance between the screen and the user's eyepoint is not a major disadvantage.
In collimated systems, the user is presented with an image which appears to be at infinity. In one type of widely used collimated system, the windows of the mock cockpit are covered by a television monitor arrangement incorporating beam splitters such that rays of light from the television monitor are reflected in a partially reflective mirror to a concave mirror and from the concave mirror back through the partially reflective mirror to the users eyepoint, Such arrangements present an appropriate image only to a user in one position and are therefore not ideal for multi-occupancy cockpit simulations as required for example for wide-bodied jets, They are used for such applications however despite the fact that two users sitting side by side only receive an appropriate image through the immediately adjacent front and side windows. A user looking towards a side or front window on the opposite side of the cockpit sees either a very distorted image or no image at all.
Collimated wider angle visual systems are known in which the cross-cockpit image problem referred above is avoided, In such systems an image is projected onto a back projection screen placed above the mock cockpit and viewed via a concave mirror placed front of the mock cockpit. The mirror is typically two or three meters away from the front of the mock cockpit but nevertheless presents an image which appears to be at infinity, Such systems now represent the majority of commercial aircraft flight simulation system but are not ideal for military aircraft simulation as the field of view in military aircraft is typically many times greater than that in civil aircraft.
The limited field of view problem referred to above can of course be overcome by increasing the size of the dome/mirror which represents the surface directly visible to the user, If the mock cockpit is stationary this is relatively easy to achieve but if the mock cockpit is mounted on a motion system the size and weight of the dome or mirror becomes a major problem as it to must be mounted on the motion system to maintain the essential geometry of the visual system.
The industry standard motion platform system referred to above typically comprises a platform mounted on six hydraulic actuators or jacks each having a stroke of about 1.5 m. Typical industry standard motion performances are set out in the following table:
______________________________________ ACCEL- DISPLACEMENT VELOCITY ERATION ______________________________________ Vertical +85.1 cm +61 cm/sec +8 m/sec.sup.2 -95.3 cm Longitudinal +102.9 cm +61 cm/sec +6.1/sec.sup.2 -150.8 cm Lateral .+-.105.4 cm .+-.61 cm/sec .+-.6.1 m/sec.sup.2 Pitch .+-.25.2.degree. .+-.20.degree./sec .+-.120.degree./sec.sup.2 Roll .+-.27.5 .+-.20.degree./sec .+-.120.degree./sec.sup.2 Yaw .+-.32.5.degree. .+-.20.degree./sec .+-.120.degree./sec.sup.2 ______________________________________
The positive and negative translational displacements in the vertical, longitudinal and lateral directions represent translational movement from a datum position to which the motion platform moves when powered up. The rotational displacements about the pitch, roll and yaw axes are also relative to axes passing thereof this datum rotation. Typically the motion platform weighs from 9000 to 12000 kg (20000 to 26000 lbs) and given the position of the motion centroid defined by the arrangement of the actuators the following typical inertia figures can be expected:
______________________________________ Roll Inertia 43000 Kg m.sup.2 (32000 slug ft.sup.2) Pitch Inertia 52000 Kg m.sup.2 (38000 slug ft.sup.2) Yaw Inertia 35000 Kg m.sup.2 (26000 slug ft.sup.2). ______________________________________
The above figures apply for motion platforms supporting visual systems capable of presenting a wide angle image subtending a field of view of for example 40.degree. vertically and 140.degree. horizontally. In a wide bodied jet simulator, a field of view of these dimensions requires a mirror which defines part of the surface of a sphere, the vertical distance between the upper and lower edges of the mirror being typically of the order of 2 m and the horizontal distance between the side edges of the mirror being typically of the order of 5 m. Doubling the vertical field of view without any increase in the horizontal field of view obviously doubles the surface area of the mirror and the structure necessary to maintain dimensional stability for the mirror is necessarily massive. Such a structure could theoretically be built but only at the expense of substantially increasing the motion platform inertia. As a consequence, when very large fields of view are required, the traditional approach has been to dispense with the obvious advantages of a full motion system and rely instead upon a stationary mock cockpit located within a stationary display incorporating for example a dome. The mock cockpit can be mounted on a vibration platform or a g-seat can be used to deliver some displacement cues to the user but the resulting system is far less realistic than could be achieved using a full motion system.
A proposal has been made to overcome the problems inherent in the provision of large field of view visual systems on a motion platform by mounting the mock cockpit on a first motion platform and a display screen in the form of a dome on a second motion platform. This proposal was the subject of a disclosure in a paper entitled "Satisfactory Visual and Motion Cueing for Helicopters/VSTOL Simulation", by S. Sexton, R. Burbidge and Dr. M. Roberts of Rediffusion Simulation Limited. That paper was presented to the Royal Aeronautical Society in May 1990. In the disclosed system the mock cockpit is mounted on a conventional six degrees of freedom motion system supported on an inclined surface and a dome is mounted on an identical second conventional motion system mounted on a facing inclined surface. The advantage of this arrangement is firstly that the dome can extend beneath the mock cockpit so as to simulation of images relevant to helicopter landing procedures and secondly that the mechanical loading on the mock cockpit motion system is reduced by the transferral of the dome structure to the second motion system. In the disclosed system, the dome is substantially hemispherical and is disposed such that the motion system supporting the dome must be rotated about the eyepoint of a user in the mock cockpit in response to pitching motions of the mock cockpit about the users eyepoint if the lower edge of the hemisphere is to remain out of the field of view of the user. Thus a relatively small rotation of the mock cockpit about the users eyepoint can result in a requirement for the motion system supporting the dome to rotate the dome about the eyepoint so that the edges of the dome traverse substantial distances. For example, if the eyepoint to dome distance is of the order of 5 m an 18.degree. rotation about the eyepoint requires a displacement of the edge of the hemisphere by more than 1 m. Clearly such displacements cannot be achieved sufficiently rapidly using standard motion system components given the large size of the display system components. Thus although the system described in the above paper has been put forward as a speculative solution to the problems associated with providing an integrated large field of view visual and motion system it has never been implemented. Alternative speculative solutions put forward in the same paper include the provision of secondary wide angle collimated displays independently mounted from a motion system, the provision of a very large static dome extending around the motion platform, and the mounting of a mock cockpit within a conventional motion platform supportive system so that the mock cockpit can be tilted relative to that motion platform.